Internal combustion engine exhaust emissions comprising hydrocarbons, CO and NO.sub.x are controlled by use of catalytic converters. The majority of hydrocarbon and CO emissions from such engines occurs within a few minutes after starting a cold engine. During start-up and warm-up while the engine is running fuel rich to avoid running or driveability problems and before the catalytic converter is heated to a sufficient temperature (light-off temperature) to reduce hydrocarbon and CO emission, the catalytic converter is not operating at a sufficiently high level of efficiency to control the emissions. To control those start-up/warm-up or hot start emissions an electrically heated catalytic converter (EHC) is located between the internal combustion engine and the standard catalytic converter. The EHC provides an active catalytic surface to convert start-up/warm-up or hot start emissions. Providing this EHC with a secondary oxygen pump to inject supplementary oxygen (air) into the exhaust gas introduced into the EHC allows for more complete combustion of hydrocarbons and CO present in the exhaust. Such pump is normally run continuously for some arbitrary pre-set time commencing at start-up. This running time is typically only about a minute. If the time selected is too short, hydrocarbon and CO emissions are not adequately controlled. If the time set is too long such that excessive air is introduced after the standard catalytic converter has warmed up and engine operation has switched to closed-loop, NO.sub.x emissions increase. The period for which the secondary air pump should run to insure maximum hydrocarbon, CO, and NO.sub.x control depends on engine type, fuel composition, temperature and the particular exhaust system. Control of the secondary air pump by arbitrarily setting a running period is not an effective control mechanism .